Manufacture of viscose



, July 14, 1931. G. w. BLANCO ET AL MANUFAC TURQ CF \"ISCOSE Filed June l2 1926 KT l 'ITORNEY Patented July 14, 1931 UNITED STATES PATENT, ori ice GALO w. BLANCO AND CARLETON HENNINGSEN, or BUFFALO, EW YomnssreNoBs, BY MESNE ASSIGNMENTS, TO nu PONT BAYON COMPANY, on NEW YORK, N..Y., A

CORPORATION OF DELAWARE madman or vrsoosn Application filed June 12,

lated in chemical constitution to the large class of compounds known as sugars or polysaccharides. No definite chemical formula can be assigned to the hemi-celluloses, as they are rather variable mixtures of compounds whose exact constitution is in many cases unknown. It has been customary to stop the operation of the press after a certain travel of the piston termed the cut-off, and to permit the liquor extracted up to this time to return to the source of supply for reuse. The press has been then put into operation again to extract the remaining liquor which is allowed to flow to waste. This operation has been followed because of the fact that the wasted liquor has been found to contain relatively high percentages (2% and over) of hemicelluloses. If hemi-celluloses are used in the steeping solution in large percentages, a number of brown gelatinized areas will appear, not only on the surface of the sheets, but extending through the sheets as well. These areas increase in number in proportion to the increase of hemi-celluloses in the steeping liquor. 1

During succeeding steps in the process of making the viscose these gelatinized areas have been found to be very detrimental. During the shredding operation the gelatinized areas, because oftheir slimy and somewhat soapy-like nature. are extremely difli- .cult to shred. Thereafter, when the alkali cellulose is treated with carbon bi-sulphide to form cellulose xanthate, the gelatinized area-s fail to react normally to the bi-sulphide. As a resultof the poor xanthation the subseuent solution in water is incomplete and thus t e viscose tends to retain the slimy aggregate v .is the cutting down of the time of ripening of which soon plugs up to a very undesirable de- 1920. Serial No. 115,478.

gree the cloths used for filtering and also the screens through which the viscose is passed before filtering. Charges which ordinarily are screened in a normal period would require three or four times as long to screen, when brown gelatinized areas were formed during steeping. It is, therefore, the custom to keep the percentage of hemi-celluloses in the canstic liquor below .5% or at the most 1%. This means that the cut-off in the steeping tank must be set at' a point which results in the waste of about one-third to one-half of the caustic employed in the press. Many schemes have been suggested to reclaim and reuse the wasted liquor most of which are expensive and unsatisfactory. 1

Therefore, one of the objects of our invention is to provide a method and a means which shallavoid the necessity of adopting such expensive methods as referred to above and which shall at the same time permit the reuse of 100% of the caustic'liquor which has formerly been wasted.

It has been found that, when all of the caustic liquor is returned to the make-up tank from the steeping press, the hemi-celluloses contained therein will gradually build up to about 3.5% and over. The percentage depends on the s ecific pulp used and may .run very high. A high percentage of hemicelluloses, however, has been accompanied with an increase in brown gelatinized areas referred to above, often as many as 7 5% of the sheets of pulp developing these areas. These areas cause the trouble in shredding xanthation' and filtration referred to above.

It has been observed, however, that the finished rayon is not harmed by the presence of the hemi-celluloses in the caustic liquor. The trouble was caused almost entirely in the operating steps.

Another object of our invention, therefore, is to provide novel and improved means which shall permit the use of a steeping caustic containing relatively high percentages of hemi-celluloses and which shall thus avoid the necessity of wasting such a'large amount of steeping liquor.

Another object achieved by our invention the steeping.

' ten to one viscose, which is one of the steps succeeding drawings in which In the accompanying for practicingwe have shown certain means our invention: 7 I

Fi re 1 is a diagrammatic plan view showing a steeping press, the tank being shown in section. Figures 2 to 5 inclusive show various means by which our invention maybe practiced.

Figure 6 is a section on the line 6--6 of Figure 5.

eferring now to the drawings in detail and more particularly to Figure 1, the numeral 1 designates the steeping tank of the press in which the raw material, in this case sheets of wood pulp, is deposited for treat ment by a bath of caustic solution. The sheets of pulp are designatedv 2 and are arranged on edge between perforated iron plates 3, which a hold the sheets upright. rom five to twenty sheets of pulp are usually placed in a compartment formed between two plates and the number of compartments isdetermined by the size of the particular" apparatus hundred. For the purpose of illustration, however, and in order to better; show the invention on a large scale, we have shown the space taken up by a comphrtment as being somewhat exaggerated. T e object of the iron plates is to. hold the pulp sheets upright and allow drainage of the. liquor.

The caustic solution is supplied. from the" make-up tank 4 and the flow to the press 1 is controlled by the valve 5. An outlet 6 is provided from the other end'of the tank and this outlet is provided with a'connection 7 leading back to the make-up tank 4 and concontrolled by a valve 8, and also with a connection 9 through which the solution ma be wasted, this connection being controlled by the valve 10. Slidably mounted in one end of the tank 1 is a piston rod 11 having a head 12 contacting with the contents of the press. The rod may be operated by any suitable 'means to compress the pulp.

In operation a solution of caustic soda of time normal strength of about 15% to 30% is maintained in the make-up tank, and this solution is run into the press through the valve 5 and to a height which will completely submerge all of the sheets 2. The sheets are left in the solution for a period which may vary from about 30 minutes to several hours in order to become thoroughly soaked therewith. Then the press is emptied of the excess solution or liquor by opening the valve 8 and per- 0 mitting the liquor to run back to the tank 4,

the valve 10 of course being closed." The piston is then moved until the head reaches some such point that indicated-by the arrow C, the length of travel of the piston head being termed the cut-oil. The liquor which is employed, and may range from:

pressed out of the sheets by this actuation of the piston is low in hemi-oelluloses, and it has been the ractice to permit this liquor to re-- turn to t e make-up tank. The remaining liquor is relatively high in hemi-oelluloses and therefore it has been the practice to waste it. Therefore, the next step in the operation has been to close the valve 8 and open the "valve 10, *after which'the piston is again actuated"t fi?pressout the liquor from the pulp. The cut-oflhas been determined by the amount of hemi-cellulose contentwhich it has been possibleto meri the -stee ing liquor without producingthepnde- We have found that the areas referred to above form on those'portions of the pulp sheets which do not have free 00-, cess to the caustic solution. The'pulp absorbs. the caustic soda solution with great rapidity.

The result is that the pulp to which the QGUStlQ solution has free access swells and tends to prevent the solution from reaching that git of the ul to which the access is more cult. t t e same time the pulp'in these 10- cali'zed areas does not react normallytothe' caustic soda. This condition results in the It has been formation of the brown areas. found that after brown areas have once been produced, subsequent steeping in caustic of normalstrength even for long riods of time will not serve to eliminate em. In other .words, the pulp is permanently. afl'ected'in these sections and cannot be; an

uently converted into an alkali-cellulose le for viscose manufacture.

It has also been discovered that number i of gelatinized areas increases proportion.

to the hemi-celluloses in the liquor.

It is believed that the increased viscosity of F:

the steeping liquor causes this. The viscosity of the steeping liquor increases rapidly as the hemi-celluloses contained therein increase,

thereby cutting down the rate at which dif fusion of the caustic to the interior portions of the sheets will take place. Thus, it becomes increasingly difiicult for solutions of higher viscosity (that is those containing large percentages ofhemi-celluloses) to penetrate completely between and into the sheets as ordinarily placed in the steeping press.

When the sheets of pulp are wetted with the steeping solution they swell very rapidly.

This swelling tends to press the sheets more closely together and tends to make the access of the solution between and into the sheets more difii'cult.

' We'have discovered that, if the pulp sheets are so placed in the press as to permit free at a access of the solution to all the sheets whereby the sheets are rapidly and'thoroughly wetted before swelling, the brown gelatinized areas are not formed. Experiments disclosed the fact that a solution containing a high content "of hemi-cellulosesthen could be used without the brown areas occurring. Therefore, by

adopting means to' insure that the caustic sobe returned to the make-up tank for reuse.

Thesaving in this respect :alone is large as indicated above. It was :found that the increased percentages of hemi c'elluloses were not only unobjectionable sofar'asthe finished rayon is concerned but that, if the brown gel atinized areas were avoided, the soakingand subse uentroperations were not adversely affecte by the presence of the hemi-celluloses.

Another feature of very great importance that has been discovered is thatthe high content of hemi-celluloses materially decreases the time necessary for ripening of viscose.- .When operatin with caustic having a high concentration hemi-celluloses, the ripening time of viscose is decreased as much as It is believed that this is due tothe presence of small quantities of hemi-celluloses which are carried down in the ulp from the steepingoperation into the .VISCOSG. The time for r pening is usually several days, and as by our invention the time has been reduced by.

approximately one-hal f,"the resultingsayin'g is arga We have found that another we .extra quantities Or, if desired, the steeping process may be carried on in the old manner and hemi-celluloses may be introduced indedependently of the steeping operation.

The means for Insuring a complete and thorough wetting, of the pulp may take a- Variety of forms. In Figures 2 to. 6 inclusive we haveshown the various means which have been tried with success and others will no doubt suggest themselves to those skilled in the art.

One means which has been fo und to be very successful is the provision ot-the sheets with corrugations. The corrugations may be arranged as desired but we have found that, when they are arranged diagonally to each edge of the sheet as indicated at 13 in Figure 2, the best results are obtained. If the'corrugations are arranged horizontally as shown at 14 in Figure 3, excellent results are also was; thetime necessar to ripen the v scose is to obtained. If the corrugationsare arranged vertically as shown a't'1'5 in Figure 4, good results are also obtained, although not so good as when they are arrangedas shown in Figures 2 and 3.

Another means is indicated in Figures 5 and 6 wherein isshown a plurality of dimples 16 formed b running the sheets through a suitable mac ine.

When any one of the embodiments illustrated is employed, itis not necessar'ythat every sheet shall be constructed as shown. We have found that it'issuffidient to have, for example every other sheet made in special form to insure free how of caustic between the sheets. means for achieving this object but obviously other forms also maybe developed by those sln'll'ed in the art without departing from the scope of our invention. Obviou ly, also,it is possible to insure the thorough wetting by separately depositing sheets of pulp or other raw material in the caustic. This operation, however, is dangerous to the operators because of the likelihood of s lashing. For that reason this method is un esirable.

In practicing our invention ,the sheets of raw material'are placed in the steeping press in the compartments asis usual. The corrugations or, other means used in place thereof will temporarily hold the! sheets in position so that the router portions thereof will be exposed to t e action of the steeping liquor. The steeping li iluor is then-permitted to enter the press. I liquor comes in contact therewith, but the he sheets swell rapidly as the means which we employ permit the liquor to come into contact. with all portions of the sheets .and thoroughly saturate. them before they swell and come in contact with one another throughout their surfaces. After the material is thoroughly steeped, the piston then is actuated to ress the material and to extract therefrom t e excess liquor, all the liquor thus extracted being returned to the make-up tank for reuse.

WVhile we have referred to the raw material. as'being made of wood pulp, it is obvious that our invention may be practiced with any other kind of raw material to which it is aplicable. We are aware that various modications and changes may be made in the practice of ourinvention as disclosed in this application and without departing from the scope of our invention. we there ore do not intend to limit ourselves except by the'appendedclaims.

Weclaimr 1. In the method of manufacturing vis-' cose" the steps which comprise wetting sheets M125;

of raw material with a steeping liquor while .holdingthe greater portions of the sheets We have shown a number of ting substantially all portions of the raw material with a. steeping liquor, steeping said material '1n 'said rliquor, extracting the in the liquor, pressingthe sheets to extr'act. theexcess liquor therefronr and reusing the liquorthus extracted for steeping other raw material. I l

,2. In themethod of manufacturing viscose thesteps which comprise placing sheets of raw material in a steeping press and with the greater portions of said sheets out of contact with one another to permit freepassage' of the steeping liquor'to all portions thereof, steeping saidoraw material in l iquor,press'ing said raw material to extract'the excess liquor therefrom, and reusing said liquor to: steep other raw material.

3. In the niethodof manufacturing viscose the steps which comprise evenly Wetting the raw material with a steeping liquor, st eeping said material in said liquor,"extracting the excess liquor. .the'r'efroimjand using the liquor thus extractedf or steeping other raw material. c

at. In the method otmanufacturihg vis cose the steps which comprise rapidly wetexcess liquor th'erefroim'and using the liquor thus'extra'cted for steeping otherv raw material. Q 7

5. In the method of manufacturing viscose the steps 'which comprise rapidly and evenly wetting 'the raw 'material with a steeping liquor, steeping 'said material in said liquor, extracting-the-excess liquor there- 7. In the method of manufacturing vis-' cose the steps which comprise rapidly and evenly wetting the raw material with a liquor containing more tharr-1% of hemicellulose, and steeping th'e'raw material in said liquor.

8. In the method of manufacturing vis cose the steps which comprise rapidly wetting substantially all portions of the raw material in the liquor containing about 3.5% hemi-cellulose, steeping the raw material in said liquor, removing the excess liquor fromc said material, and using the liquor'thus extracted to steep other raw material.

9. In the method of manufacturing viscose the steps which comprise evenly wettingthe raw material int e liquor, containingabout 3.5% hemi-cellulose, steeping the raw-material in said liquor, removing the excess'liquo'r 'from said material, andusing 'matria'l;

10. Inthe method an; liquor thu x t rac dlt sheep of. manufacturing viscose, the steps which, comprise wetting sheets ofraw mater1a-l w1th asteep'ing llq'uor containing more than-1% of hemi-cellulose while holding the greater portions of the sheets out, Off .Contact' with one another to permit the free passage of the stee ping liquor to substantially all portions thereof, steepingsaid sheets inlthe liquor, pressing the sheetsto extract the excess liquor therefrom and using the liquor'thus extracted for steeping other raw material.

'11. In the method of, manufacturing viscose, the steps which comprise wet-ting sheets of raw material with a steeping liquor containing approximately 3 4. hemi-cellulps'e' while holding the greater portions of the sheets out of contact with one another 'to permit free circulation of'the steepin liquor to substantially all portions thereo steeping said sheets in the liquor, pressing the sheets to extract the excess liquor therefrom and reusing the liquor thus extracted for steeping other raw material.

12. In the'method of manufacturing "viscose, the step which comprises wetting sheets of raw material with a steeping liquor while holding the greater-portions of the sheets out of contact with one another to permit free. passage of the steeping liquor to substantially all portions thereof.

13. In-the method of manufacturing viscose, the step which comprises wettingshcets, of raw material with a steeping liquor containing more than 1% of hemi-c-ellulose while holding the greater portions of the sheets out of contact with one. another to permit free passage of the steeping liquo to substantially all portions thereof;

145111 the method ofma-nufacturing viscose, the step which comprises wetting sheets of raw material with a steeping liquor containing approximately 3 of hemi-cellulose while maintaining the greater portions 'of the sheet-sout of contact with one another to permit free'passage of the steeping liquor to substantially all portions thereof.

In testimony whereof, we have affixed our signatures to this specification.

'GALO BLANCO.

CARLETON HENNINGSEN. 

